The Shadow Booster is one of, and arguably the second-most powerful, the Five Boosters of Balance. Currently Moordryd Paynn is the Shadow Booster, as revealed in Episode 27: Paynn Rising. He uses an amulet that is possessed by Armeggaddon in conjunction with the Black Draconium Gauntlet of Sight to achieve his transformation.
The Shadow Booster's primary draconium influence is black, one of the most influential of the draconium colours. The armour of the Shadow Booster is depicted with dark colours of purple, maroon and black, with grey-plated, black shoulder pads and gauntlets, and the Dragon Eye symbol directly in the middle of the chest. A full-face black mask with a flowing purple "tail" behind it is placed on the Shadow Booster's head, and the eyes glow with fire, much like Armeggaddon's.
Moordryd receives the amulet from Armeggaddon in Episode 22: Still Waters Freeze and is lead to the gauntlet in episodes 25 and 26. His dragon, already being of pure black draconium after the events in Episode 24: When Darkness Falls, later absorbs the bone-mark of the Vysox, and this form is revealed each time Moordryd activates the armour.
Historically, while as far as viewers know, the original Dragon and Shadow Boosters shared the same enmity that the current ones do, and at one point had to join forces, as seen in Episode 38: Battle for the Ages, to get themselves out of a sticky situation involving an army of orange dragons. Despite being supposed enemies, they must have eventually worked together to stop the Dragon-Human War, and both Artha Penn and Moordryd are shown throughout the final episodes of the series to begin working together just as the ancient Boosters did.